Semiconductor integrated circuit designs and manufacturing techniques continue to evolve. Great progress has been made over the past generation in all phases of integrated circuit manufacturing to improve reliability of the finished products. Reliability of integrated circuits is of paramount importance to all concerned: the manufacturer, the OEM customer, and the end user. Indeed, in some "mission critical" applications, such as medicine or extra terrestrial applications, reliability of such circuits can be a matter of life and death. Even in more pedestrian applications, circuit failures lead to wasted time and expense, not to mention erosion of the manufacturer's reputation.
Although, in general, reliability of integrated circuits has become very high, the relentless push toward higher levels of integration, while maintaining high levels of reliability, presents an ongoing challenge. Part of the integrated circuit manufacturer's quest to improve reliability involves failure analysis--the analysis of failed parts in order to determine what caused the failure. Most manufacturers have extensive failure analysis departments, staffed by technicians, engineers, and other professionals who are skilled in this specialty.
Traditional methods of failure analysis include the following: applying selected voltages to circuit inputs and examining selected output voltage levels, either through the use of a functional tester, mechanical probing system, or the use of an electron beam detection system. Another known method of failure analysis is to apply selected voltages at certain pins and measure the current that the integrated circuit ("IC") draws in response. Another method involves applying selected currents at certain inputs and measuring the voltage levels or applying selected voltages to predetermined pins and looking for "hot stops" on the IC through either emission microscopy or infrared detection systems.
ICs fail in a variety of modes and for a variety of reasons. Many times, the IC does not fail until after it has been mounted on a printed circuit board ("PCB"). When the IC fails in this manner, the customer typically removes and replaces the IC from the PCB before sending the failed IC back to the manufacturer for failure analysis. To detach the IC from the PCB, the solder used to attach the failed IC to the PCB is heated and removed. This process often leaves excess solder on the leads of the failed IC.
The excess solder left on the leads of the failed IC must be removed before the IC is tested. Excess solder on the leads of the IC can cause adjacent leads to short which can lead to erroneous failure data and permanent damage to test equipment such as functional testers. Excess solder can also cause intermittent failures by intermittently shorting adjacent leads together. Intermittent failures are often difficult to detect and thus, time consuming, because they depend not only on the electrical signals being applied to the IC but also on the mechanical forces which cause the excess solder on adjacent leads to touch, intermittently shorting together. Excess solder also prevents failed ICs from being received into the IC sockets used in some test equipment, including functional testers. Current IC package technologies have leads that are extremely close together and the IC socket which receives the failed IC has equally close lead connections. Introducing failed ICs having excess solder on the leads into sockets often results in bending the relatively fragile IC leads.
Excess solder is ordinarily removed from the leads of ICs using a soldering iron and a "solder suck". The soldering iron is a manual device having a heated metal tip which melts or softens the excess solder when it is touched to the leads of the ICs. The solder suck is another manual device which creates an air vacuum that removes or "sucks" the melted or softened solder off the leads.
A primary disadvantage or limitation of removing excess solder in this manner is that it is time consuming. To avoid damaging the IC, excess solder must be removed generally from one lead at a time. Often, a single heat-and-suck cycle is insufficient to remove all of the excess solder requiring the technician to repeat the process many times.
In addition, removing solder using a soldering iron and a solder suck can result in damage to the IC. The technician generally holds the soldering iron in one hand and the solder suck in the other hand because the solder must be removed while it is still in a melted or molten state. This process requires excellent hand to eye coordination to heat the solder a sufficient amount of time quickly followed by activating the vacuum action of the solder suck to remove the excess solder. If the soldering iron is left on the lead for a longer than necessary time to melt the excess solder, the heat can damage the internal circuitry of the IC. Also, the solder suck vacuum action must be activated at the right time. If the solder is not sufficiently melted when the solder suck is activated, the solder will not depart the lead.
The leads of an IC can also bend when soldering irons and solder sucks having tips with diameters many times larger than the lead pitch of the ICs are applied incorrectly to the IC to remove the excess solder. Yet another problem with using a soldering iron and a solder suck to remove excess solder is that the technician may not be able to visually determine whether all of the excess solder is removed from the IC leads. This method of removing excess solder from the leads of failed ICs is thus time consuming and can itself introduce defects into the IC rendering the failure analysis suspect, if not useless.
Accordingly, it would be desirable to remove excess solder from ICs quickly, efficiently, and repeatably without damaging the IC. Additionally, it would be desirable to remove excess solder from ICs without the use of cumbersome solder removing tools like a soldering iron and a solder suck.